1. Field of the Invention
The present invention generally relates to a finite linear rolling guide for guiding a movable body, such as a table or saddle of a machine tool. More specifically, the invention relates to a method and an apparatus for carrying out a correcting operation for returning a relative positional relationship between a movable body and a finite type rolling guide to a normal positional relationship, when the relative position of the movable body to the finite linear rolling guide changes gradually to shift the finite type rolling guide from an appropriate position while the movable body continues a reciprocating motion.
2. Description of the Prior Art
Guides for movable bodies, such as tables and saddles of machine tools, include slide linear guides, static air pressure linear guides, static oil pressure linear guides and finite linear rolling guides. Of these guides, finite type rolling guides can ensure the rigidity of machines, and the number of auxiliary facilities required for finite linear rolling guides is smaller than that for static pressure guides, so that finite type rolling guides are effective for space saving for machines and are effectively used as ultraprecise machine elements. For that reason, finite linear rolling guides are often utilized as guide machine elements for small ultraprecise finishing machines.
FIG. 7 shows an example of a conventional finite linear rolling guide which is disclosed in Japanese patent laid-open 2000-202727. In FIG. 7, a bed 1 of a machine tool is formed with V-shaped grooves 2, and rolling guides 3 are provided so as to extend along slant faces of the V-shaped grooves 2, respectively. On the bottom face of a table 4 as being a movable body 4, there are formed slide portions 5, each of which has a shape corresponding to a corresponding one of the V-shaped grooves 2. Each of the slide portions 5 is designed to contact a corresponding one of the rolling guides 3.
Each of the rolling guides 3 of this finite linear type comprises a bearing consisting of a combination of a retainer and a roller. In general, each of the rolling guides 3 is only supported on a corresponding one of the V-shaped grooves 2 without being fixed thereto.
Therefore, if the table 4 moves, there is caused a phenomenon that the rolling guides 3 move, little by little, in the opposite direction to the moving direction of the table 4 as a whole. If the reciprocating motion of the table 4 continues for a long time, the deviation in the relative positional relationship between the table 4 and the rolling guides 3 gradually increases. If this deviation in position is left as it is, there are some cases where the table 4 finally falls away from the rolling guides 3.
In order to prevent the deviation in position of the rolling guide 3, an operator monitors the operation of the machine, and when the deviation in position of the rolling guide 3 increases to some extent, the operator suspends the operation of the machine and manually moves and adjusts the table 4 so as to return the relative positional relationship between the rolling guide 3 and the table 4 to a normal positional relationship. There is also known a mechanical positioning mechanism capable of adjusting the position of the rolling guide along the V-shaped groove.
However, if the operator must manually adjust the deviation in position of the rolling guide 3, the operator must be always be on standby to prepare for the above mentioned problem. So there is a problem in that it is not possible to realize an unattended operation in the case of an ultraprecise machining which takes a lot of time to complete a process for a workpiece.
In addition, in ultraprecise finishing machines utilizing rolling linear guides, the feed rate of a movable body, such as a table, increases with the request for the increase of efficiency. In recent years, the feed rate is generally about 10 m/min. However, in the reciprocating motion of the movable body, the rate of the movable body in the approach route is high, whereas the rate of the movable body in the return route is low. Therefore, due to the large difference between the rates in the approach and return routes, the deviation in position of the rolling guide 3 is greater than that in conventional machines.
Moreover, if the rolling guide 3 is provided with a position adjusting mechanism, this position adjusting mechanism requires a rack, a pinion and a running block, and causes large vibrations during positioning, so that there is a problem in that such a position adjusting mechanism can not be applied to ultraprecise finishing machines.
It is therefore an object of the present invention to eliminate the aforementioned problems and to provide a finite linear rolling guide deviation correcting method and apparatus capable of detecting a relative positional relationship between a rolling guide and a movable body if the relative positional relationship increases, and automatically carrying out a correcting operation for returning the relative positional relationship to a normal positional relationship.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, there is provided
a method for correcting a relative positional relationship between a finite linear rolling guide and a movable body guided by the finite linear rolling guide, the finite linear rolling guide having a row of a plurality of rolling guides arranged in a direction of the reciprocating motion of the movable body, said method comprising the steps of: detecting whether the rolling guide remains beneath one end portion of the movable body in a forward direction, of both end portions of the movable body in moving directions; Determining that the positional deviation of the finite linear rolling guide increases when no rolling guide can not be detected; changing the moving direction of the movable body into the backward direction; correcting the deviation in relative position between the movable body and the finite linear rolling guide by moving the movable body to a stroke end of the movable body.
According to another aspect of the present invention, there is provided a apparatus for correcting a relative positional relationship between a finite linear rolling guide and a movable body guided by the finite linear rolling guide, the apparatus applied for the numerically controlled machine tool having a numerical control unit, a feed mechanism for the movable body, said apparatus comprising: a finite linear rolling guide having a row of a plurality of rolling guides arranged in a direction of the reciprocating motion of the movable body; detecting means disposed in both end portions of the movable body in moving directions, for detecting whether the rolling guide remains beneath one end portion of the movable body in a forward direction; correction control means for determining that the positional deviation of the finite linear rolling guide increases when no rolling guide can not be detected, and generating a correction signal to change the moving direction of the movable body into the backward direction so that the deviation in relative position between the movable body and the finite linear rolling guide is corrected; and servo control means for controlling a servo motor which drives the feed mechanism based on the correction signal provided by the correction control means.